Wood strain insulator



Dec. 27, 1927.

1,654,286 L. E. FROST WOOD STRAIN INSULATOR Filed March 14, 1921 WITNESSES: INVENTOR Leslie Lip/"067':

ATTORNEY Patented Dec. 27, 1927.

UNITED STATES PATENT OFFICE.

LESLIE E. FROST, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHQUSE ELECTRIC & MANUFACTURING COMPANY, A C({RPORATION OF PENNSYLVANIA.

WOOD STRAIN INSULATOR.

Application filed March 14, 1921. Seria1 No. 452,198.

My invention relates to composite articles, more especially to composite wood strain insulators for use on trolley and transmission lines of relatively high-voltage 5 capacity and to amethod of forming the same.

Heretofore, it was customary to employ kiln-dried hard woods, which were treated with asphaltum gums to make them moisture 1Q repellent, for insulatorson relatively highvoltage transmission lines. It was very diflicult to get uniform and deep impregnation in every instance and, because of this deficiency, such insulators frequently failed in service because of the absorption of moisture. I

As an improvement over this method, it has been proposed to first impregnate kilndried wood with paraffin and then impregnate it with a moisture-proof gum, the object of this double impregnation being to obtain a deeper penetration of the impregnating materials, thereby obtaining greater uniformity in quality. This method, al-

though more dependable than the former,

is somewhat complicated.

My invention obviates these difliculties, it being among the objects thereof to form strain insulators in an eflicient and simple so manner.

It is a further object of this invention to form composite wood strain insulators which are moisture proof, which have a high dielectric strength, which are mechanically strong and which will not deteriorate under varying atmospheric conditions. i In practicing my invention, I provide a body of hard wood, preferably maple, which is thoroughly dried by baking for approximately twelve hours at 100 C. I then apply one coat of insulating varnish, such as spar varnish, which is ,hardened by baking in an oven. Next, the body is placed between the rotating centers of a lathe and a coat of spar varnish is applied with a brush or in any other suitable manner. While the varnish is in a tacky or plastic condition, I wind a strip of cloth impregnated with a varnish, such as a copal gum and linseed oil varnish, helically around the outer surface and then apply another coat of spar varnish on the surface thereof. This process is repeated until a suitable number of layers of treated cloth material has been formed and a,

coating of spar varnish .is applied. The

structure is then baked to harden the varnish. I then swage a metallic member or cap on each end of the insulating member, and, to further protect it, I apply a number of coatings of weatherproof paint.

In the accompanying drawings part hereof and in which like characters designate like parts,

Figure 1 is a cross-sectional view of a wood strain insulator made "in accordance with my invention,

Fig. 2 is va sectional view thereof along the line IIII of Fig. 1, and

Fig. 3 is a sectional view of the insulator along the line III-III of Fig. 1.

I provide a body of wood 1, preferably hard maple, which I thoroughly dry by heating for twelve hours at a temperature of 100 C. I apply a coating of spar varnish upon thesurface 2- thereof and then bake the varnish to harden it. The member 1 is mounted between the rotating centers of a lathe and another coating of spar varnish is applied and a strip of cloth impregnated with an insulating varnish is wound helically along the surfaceQ, forming a layer 3, which is again coated with a layer of spar varnish and another layer of impregnated cloth is wound thereon. This process may be repeated as many times as is desired, usually three or four layers being suflicient. I then apply a coating of spar varnish to the surface of the structure and subject the same to heat in an oven fora suitable length of time, to harden the varnish, making the structure moisture proof. I further provide a pair of metallic members 4 and 5, which I swage on the tapered ends 6 and 7 of the body 1 and then apply .a number of coatings of weatherproof paint to the insulator to further PIQ." tect it against atmosphericconditions.

," Although I have described a specific embodiment of my invention, it will be obvious to those skilled in the art that va- 100 rious' modifications may be made therein without departing from the principles herein set forth. For instance, I may substitute any suit-able insulating resins or varnishes, such as phenolic condensation prod- 105 ucts, casein, blood glues and the like for the spar or insulating varnishes. I may further swage the end members on the ends of the insulator before winding the treated cloth thereon or I may employ any number of 110 forming a reference layers of cloth with alternating layers of varnish coatings.

It will be seen from the above description of my invention that wood strain insulators formed in this manner are highly moisture repellent and possess relatively high dielectric strength, one-of the important advantages being that wood strain insulators made by this process are uniform in quality and reliable in service.

I claim as my invention 1. A composite article comprising a body of wood having a layer of insulating varnish thereon and a plurality of alternate layers of sheet insulating material and insulating varnish formed thereon.

2. A composite article comprising a body of wood having a plurality of coatings of insulating varnish and a plurality of layers of sheet insulation material alternately formed on the surface thereof in the order named.

8. A method of forming composite articles which comprises providing a body of wood, drying said wood by heating iir an oven, coating the outer surface thereof with a varnish, hardening said varnish by baking, applying another coat of varnish, winding a strip of fibrous material around said body of wood on said varnish while plastic, applying a coat of varnish on said wound strip and baking to harden the surface.

4c. A method of forming composite articles which comprises providing a body of hard wood, drying said hard wood by heating in an oven at a temperature of 100 (1,

coating the surface thereof with an insulating varnish, hardening said varnish by baking in an oven, applying a coat of insulating varnish, winding a strip of cloth around said body while the Varnish is plastic, applying another coating of insulating varnish and another layer of cloth, and apply ing another coating of varnish and heat a hardening the same by baking.

In testimony whereof, I have hereunto subscribed my name this 28th day of February, 1921.

LESLIIQ E. FROST. 

